Simultaneous Promotion of the Mechanical Flexibility and Dielectric Strength of Impact Polypropylene Copolymers Containing Multifold H‑Shape Long-Chain-Branching Structures for Recyclable Power Cable Insulation Application

In the synthesis of impact polypropylene copolymers (IPCs) containing multifold H-shape long-chain-branching (LCB) structures by synchronizing IPC production with ω-alkenylmethyldichlorosilane copolymerization-hydrolysis (ACH) chemistry, some small amounts of ethylene are introduced into the first-stage propylene polymerization to tune the chain structure of the polypropylene (PP) matrix, aiming to promote the innovated heterophasic copolymers in mechanical flexibility with collateral damage on electrical properties minimized. This has resulted in the incorporation of a few ethylene units into the otherwise net PP matrix that significantly reduces the average sequence length of PP chains, leading to a profound increase in mechanical flexibility. To one’s surprise, such a mechanical flexibility enhancement has not been, as previously hypothesized, compromised by loss of dielectric strength. As a matter of fact, simultaneous enhancements in both mechanical flexibility and electrical breakdown strength have been achieved with the long-chain-branched IPCs (LCB-IPCs) incorporated with ethylene in the PP matrix. The LCB-IPCs with ethylene-incorporated PP matrices are also characterized by the many structural and property privileges ascribable to their multifold H-shape LCB structures, including fine spherulite morphology, fine and stable rubber phase dispersion morphology, strong interfacial adhesion, and the resulting high elongation ratio, high electrical breakdown strengths under both alternating current (AC) and direct current (DC) electrical voltages, and excellent elongational flow properties characterized by strong strain-hardening effect, all benefiting potential power cable insulation applications.